The present invention relates to methods and apparatus for measuring a chemiluminescent signal from a solid surface. In particular, the present invention relates to methods and apparatus for use in heterogeneous immunoassays wherein a chemiluminescent signal provided by the immobilized product of an immunochemical reaction from a solid, porous matrix is measured.
Several automated chemiluminescence instruments use photographic means and a densitometer for recording signal. Vogelhut, U.S. Pat. No. 4,231,754; Whitehead, et al., U.S. Pat. No. 4,593,728; Thorpe, et al., Clin. Chem., 30, 806, (1984); and Bunce, et al., Analyst, 110, 65 (1985).
Clear coated microtitration plates as a solid phase with trigger solution port and detector at opposite sides of the plate well may also be employed in such instruments. Holley, European Patent Application 025,350; and Schroeder, et al., Clin. Chem., 27, 1378-1384 (1981). This technique is severely limited due to the slow reaction rates resulting from the limited diffusion of analyte molecules to the capturing solid phase. Use of this approach has been of limited sensitivity and is generally employed in reactions involving the use of ATP and luminol-type tracers.
Magnetizable microparticles and magnetic separation in a test tube may be followed by reading the signal of the suspended particles in a tube luminometer as is found in the commercially available Magic.TM. Lite system distributed by Ciba-Corning Diagnostics. Because the brown colored microparticles optically interfere with the chemiluminescent signal, a very low mass of these particles is used. This leads to very slow reactions. For example, an assay for thyroid stimulating hormone (TSH) is reported to have a three-hour incubation time. In addition, many manipulation steps are involved, making this assay configuration difficult to automate. Other luminometers in which the signal is generated in a test tube are sold by Berthold, Hamilton, Turner Design and Analytical Luminescence.
Enhanced chemiluminescent reactions in a white microtitration plate followed by reading the generated signal in a luminometer having a moving mask and photomultiplier tube are described in Lisenbee, et al., European Patent Application 194,102 and are incorporated in the Amerlite.TM. system sold by Amersham Inc. This latter technique suffers from the same limitations of an ELISA assay in a coated plate, namely the slow diffusion rate of the reactants to the capture phase.